Various types of roof supporting structures have hitherto been proposed, including rafter-purlin systems which utilize essentially linear or one-way structural members and three-dimensional interlocking trusses which form a grid structure. One-way purlins or joists are laterally unstable and to overcome such instability it is necessary to install bracing members between the purlins or joists. This adds materially to the cost of the roof structure in that the bracing members must be individually installed on the job site after the one-way structural members have been put in place. In the case of three-dimensional interlocking trusses, or space grids, while such structures are highly efficient and capable of carrying loads both longitudinally and laterally, they are costly to manufacture and install and hence are not competitive with purlin or joist systems.
A number of the difficulties inherent in roofing systems of the foregoing types have been overcome by the integrated roofing system taught in copending application Ser. No. 143,261, filed Apr. 24, 1980, and entitled "Integrated Roof System", now U.S. Pat. No. 4,349,996. This system utilizes a series of V-trusses extending between the supporting rafters at spaced apart intervals, the V-trusses being arranged in aligned rows. Seats are provided to anchor the V-truss units to the rafters, and when installed the V-truss units are independent of each other and do not require interconnecting bracing. With this system, the V-truss units may be pre-fabricated and hoisted into position between the rafters with the opposite ends of their top chord members supported by the seats which are secured to the rafters. Since cross-bracing between adjoining V-trusses is not required, the cost of this system is materially reduced.
While the aligned V-truss system is self-bracing and has a high capacity for gravity and uplift loading, it must nonetheless rely on either the roof deck or additional diagonal bracing for lateral load (shear) resistance. In this connection, it will be understood that the roof deck is composed of interconnected roofing panels which are secured to the top chords of the V-trusses by means of concealed fasteners, such as those taught in U.S. Pat. No. 4,102,105, issued July 25, 1978. Such concealed fastener roof systems have limited shear capacity because the fasteners permit some slippage to occur between the roof panels and the supporting trusses or purlins.
The present invention is directed to a V-truss roofing system in which the rows of trusses are arranged in alternating relation so as to develop shear load capability by transferring horizontal forces through the alternating V-trusses to the walls of the structure. The structure thus has the capability of transferring a wind load acting on a given wall of the structure to adjoining walls.